About 200 protesters shouted "Allah-o-Akbar" (God is great) outside the court when the ruling was announced.

"You can't at whim and fancy convert from one religion to another," Ahmad Fairuz said.

Ms Joy's case has tested the limits of religious freedom in Malaysia.

She started attending church in 1990 and was baptised in 1998.

In 2000, Ms Joy, 42, went to the High Court after the National Registration Department refused to remove "Islam" from the religion column on her identity card. The court said it was a matter for Sharia courts. Tuesday's ruling marked the end of her final appeal.

Ms Joy has been disowned by her family and forced to quit her job. She went into hiding last year. A Muslim lawyer who supported her case received death threats.

Sharia courts decide on civil cases involving Malaysian Muslims - nearly 60% of the country's 26 million people - while ethnic minorities such as Chinese and Indians are governed by civil courts in the multi-racial country.